Various methods are known for making channeled materials. J. Reeman, R. W. Buswell and D. G. Ainley described the method of producing cooling passages in high-temperature turbine blades by the incorporation of cadmium wires in the blade pressing and their subsequent removal by evaporation during sintering, as reported and cited in "Fundamental Principles of Powder Metallurgy" edit by W. D. Jones, and published by Edward Arnold Publisher Limited, London 1960, page 341. This method is very labor and time consuming and does not allow the manufacture of micro-channeled materials with small and uniformly distributed channels.
A directional solidification method called GASAR has been developed for producing solids with controlled porosity 1-3! as disclosed in U.S. Pat. No. 5,181549 issued Jan. 26, 1993. Metals are melted in a given atmosphere of a gas (usually hydrogen), poured into a mold while subjected to a desired pressure, and cooled. As the metal solidifies, the solubility of the dissolved gas goes through a sharp decrease and bubble nucleation occurs. Bubbles which form in the liquid float to a hotter region and are reabsorbed. Bubbles which form at the solid-liquid interface may grow as either isolated or continuous porosity, depending on the solidification conditions. The final microstructure of the porous materials depends on both thermodynamic and kinetic processes. Homogeneous nucleation of bubbles under GASAR processing conditions is impossible, the process is limited to systems which do not form hydrides, the eutectics are highly asymmetric, which leads to an extremely small range of compositions and solidification temperatures where stable eutectic growth is possible. This method does not allow the manufacture of long structures with through microchannels of a given diameter. Moreover, this method cannot be used for producing channels oriented in two or more desired directions.
U.S. Pat. No. 4,818,264 issued Apr. 4, 1989 to Marsha L. Langhorst discloses that hollow glass fibers have been made by drawing down tubes which can be used to produce glass polycapillary materials. Seven glass tubes, 1.8 mm outside diameter by 1.4 mm inside diameter, were placed inside an 8 mm outside diameter by 6 mm inside diameter glass tube and this assembly was drawn with a glass tube drawing machine. The subject patent cites an article by H. D. Pierce Jr. Et al, Technical note "A method for the Preparation of Glass Multicapillary Columns", vol. 17, J. of Chromatographic Science, 5/79, 297, as the source of this work. This method cannot be applied to the powder or brittle materials, such as ceramics, intermetallics, carbon, etc.
Extrusion method for forming thin-walled honeycomb structures was developed by D. Rodney et al. as disclosed in U.S. Pat. No. 3,790,654 issued Feb. 5, 1974. Rodney et al disclose the use of an extrusion die having an outlet face provided with a gridwork of interconnected discharge slots and inlet face provided with a plurality of feed openings extending partially through the die in communication with the discharge slots. Extrudable material is fed to the die under pressure wherein the extrudable materials flow to the interconnected discharge slots communicating with the outlet face, wherein a portion of the material flows laterally within such slots to form a continuous mass before being discharged longitudinally therefrom to form a thin-walled structure having a multiplicity of open passages extending therethrough. The longitudinally discharged mass is rigidified to prevent deformation of the passages. The disadvantage of this method is a very complicated and very expensive tooling, which does not allow the production of the channels less than 0.5-1 mm in diameter and interchannel walls less than 0.2 mm in diameter nor does it allow the production of structures with channels oriented in two or more directions.
Although not concerned with the manufacture of channeled materials, it is noted that some of the procedures used in carrying out the present invention to produce channeled structures, are also used in making monolithic fibrous ceramic structures, as described in U.S. Pat. No. 4,772,524 issued Sep. 20, 1988 to William S. Coblenz.
The Coblenz patent discloses a method of producing fibrous monolithic ceramic product of high density. This product is formed of a plurality of coated fibers and each coated fiber comprises a ceramic core with a ceramic coating. The green body of ceramic materials from which the product is formed is plastically deformed and densified by sintering. However, there is no disclosure or suggestion in this patent for using procedures to produce a multi-channeled structure such as that disclosed and claimed herein.
U.S. Pat. No. 4,965,245, issued Oct. 23, 1990 to Masaru Sugimoto et.a., discloses a method of producing a superconducting cable or coil comprising a bundle of coated metallic filaments, for example, coated with an oxide, that are drawn and heated in oxidizing atmosphere to form a superconductor. Again, this patent neither discloses nor suggests a process for making channeled structures as disclosed and claimed herein.